Identification of red high proper-motion objects in Tycho-2 and 2MASS catalogues using Virtual Observatory tools

摘要

Aims. With available Virtual Observatory tools, we looked for new M dwarfs in the solar neighbourhood and M giants with high tangential velocities. Methods. From an all-sky cross-match between the optical Tycho-2 and the near-infrared 2MASS catalogues, we selected objects with proper motions μ??>??50?mas?yr-1 and very red VT???Ks colours. For the most interesting targets, we collected multi-wavelength photometry, constructed spectral energy distributions, estimated effective temperatures and surface gravities from fits to atmospheric models, performed time-series analysis of ASAS V-band light curves, and assigned spectral types from low-resolution spectroscopy obtained with CAFOS at the 2.2?m Calar Alto telescope. Results. We got a sample of 59 bright red high proper-motion objects, including fifty red giants, four red dwarfs, and five objects reported in this work for the first time. The five new stars have magnitudes VT??≈??10.8–11.3?mag, reduced proper motions midway between known dwarfs and giants, near-infrared colours typical of giants, and effective temperatures Teff??≈??2900–3400?K. From our time-series analysis, we discovered a long secondary period in Ruber?4 and an extremely long primary period in Ruber?6. With the CAFOS spectra, we confirmed the red giant nature of Ruber?7 and 8, the last of which seems to be one of the brightest metal-poor M?giants ever identified.